Adgeneration: rewrite adapter to match Prebid.js v1.6.6 spec

[ss-toshihide-tajima]

Summary

This PR modernizes the Adgeneration adapter, which has not been updated in several years and has diverged from our Prebid.js adapter. It brings the server-side adapter into parity with Prebid.js v1.6.6 (modules/adgenerationBidAdapter.js) and moves it to the endpoint our ad server now serves for Prebid traffic.

We (Supership Inc.) are the maintainer of this bidder (ssp-ope@supership.jp).

Changes

• Switch the endpoint from GET /adsv/v1 (query parameters) to POST https://d.socdm.com/adgen/prebid (JSON body) — the same protocol the Prebid.js adapter uses
• Add native support for both site and app; banner is kept. Video is intentionally not declared, matching Prebid.js (supportedMediaTypes: [BANNER, NATIVE]): VAST creatives are delivered wrapped as banner
• Detect the request origin from ext.prebid.channel / BidRequest.App and device.os, and forward it as the sdktype query parameter (web / Prebid Mobile Android / Prebid Mobile iOS) so the backend can distinguish delivery paths
• Percent-encode VAST XML embedded in JS string literals for Prebid Mobile iOS (WKWebView) compatibility
• Forward dealid from the backend response as bid.dealid
• Rename the builder struct to adapter per the repository semgrep conventions
• Rewrite the JSON golden files for the new protocol and add a native exemplary test; adapter coverage is 97.6%

Publisher impact

None expected. The bidder params are unchanged (id, required, string). PBS hosts running older versions keep working: the backend continues to serve the legacy /adsv/v1 endpoint during the transition.

Testing

• ./validate.sh --nofmt --cov --race 10 passes locally
• Verified end-to-end against the production backend from a test PBS host: web (S2S) and app (Prebid Mobile SDK on Android and iOS) requests all receive and render bids

Docs

prebid/prebid.github.io#6665 (companion docs update: pbs: true, pbs_app_supported: true, media_types: banner, native)

[ss-toshihide-tajima]

Hi @bsardo, a gentle follow-up on this PR 🙏

We (Supership) maintain the Adgeneration bidder, and this PR brings the server-side adapter into parity with our Prebid.js adapter — we've been maintaining the Prebid.js side under this same handle (e.g. prebid/Prebid.js#12538, which introduced the endpoint/protocol this PR now adopts on the server side). Is there anything needed from my side to get it into the review queue?

One small ask in the meantime: since this is our first contribution to this repo, the Validate and adapter-code-coverage workflows are still awaiting maintainer approval to run. Could someone approve the workflow runs so the CI results are visible? (./validate.sh --nofmt --cov --race 10 passes locally.)

Happy to address any feedback. The companion docs PR is prebid/prebid.github.io#6665.